A novel method of allelic exchange has been developed. This method is demonstrated in E. coli with the use of a mutant luciferase gene. The mutant luciferase gene had a termination codon placed in frame at the glutamine 143 amino acid. An exchange for the normal gene was demonstrated in E. coli. The exchange required the use of an oligonucleotide, and the very short repair enzyme (vsr). Through an unknown mechanism, an oligonucleotide with the correct sequence to restore glutamine 143 was capable of binding to its complementary strand and the vsr enzyme enabled the exchange of genetic information between the two different genes. The efficiency of exchange is not high. It is at 0.15% of the total possible light emission for the correct gene. Continued work on this assay is planned to broaden the scope of mutations that can be assayed using additional enzymes that recognize and hydrolyze mismatched base pairs of DNA such as the E. coli MutY enzyme, which recognizes C/A and G/A mismatches in heteroduplex DNA.